Need a Refill?

A refresher course on how much—and what—to drink on hot summer runs.

During the blazing days of summer, you need more than sunscreen to protect your body from the sun. "Hydration becomes most important during intense exercise in the heat," says Douglas Casa, Ph.D., who heads the University of Connecticut's Korey Stringer Institute, which studies heatstroke and other causes of sudden death in sports. "If you're not adequately hydrated, your blood volume drops, which means your heart has to work harder to power your muscles and keep you cool. When that happens, your running performance suffers."

While it's important to stay hydrated during exercise, it's impossible to create one-size-fits-all drinking guidelines. Every runner's needs are different. Your body weight, sweat rate, and effort level, along with the temperature, humidity, and elevation, affect how much you should drink. That doesn't mean you should leave your hydration plan up to chance. These strategies can help ensure you drink the right amount before, during, and after every run.

Before Your RunOne of the best ways to limit dehydration during a run is to drink enough before it. "Checking your urine prerun is an easy way to see if you're hydrated," says Lewis Maharam, M.D., former medical director of the Rock 'n' Roll race series. "If it's clear, you're drinking too much. If it's the color of iced tea, you need to drink more. If it's a pale lemonade or straw color, you're nicely hydrated."

How much you should drink depends on how soon you'll be running, what your stomach can tolerate, and how dehydrated you are. "Typically, most people can handle six to eight ounces right before a run," says Heidi Skolnik, M.S., C.D.N., owner of Nutrition Conditioning in New York City. With the exception of alcohol, which is dehydrating, all beverages, including water, sports drink, coffee, tea, juice, and milk, can help keep you hydrated throughout the day.

If you find you're often dehydrated before a run, make sure to have a beverage with all your meals. "The fluid you drink helps you absorb the water content in whatever you eat," says Skolnik.

During Your RunIf you're headed out for an 18-miler, drinking midrun is a no-brainer. But what if you're going for an hour? Or doing 45 minutes of intervals? "There have been a range of recommendations over the past two decades," says Dr. Maharam. "The newest brings us back to basics: Drink to your thirst." It's advice backed up by the International Marathon Medical Directors Association and Tim Noakes, M.D., author of Waterlogged: The Serious Problem of Overhydration in Endurance Sports. "Your thirst mechanism is exquisitely tuned to your body," says Dr. Noakes. "Some runners get thirsty quickly; others can go hours without feeling the need to drink much. If you drink when you're thirsty, you'll stay adequately hydrated." That said, Casa and Skolnik suggest always drinking on runs 90 minutes or longer.

The American College of Sports Medicine offers another approach; it recommends drinking enough so you don't lose more than three percent of your weight through sweat. "Lose more than that and your performance starts to falter," says Casa. One way to figure out how much you lose during an hour of running is to conduct a sweat test: weigh yourself naked before a run, then during the run keep track of how much you drink. Weigh yourself naked again postrun, adding the amount you drank to your weight loss. (For example, if you lost one pound but drank eight ounces it means you sweated 24 ounces in one hour.) "The goal isn't to match that loss during a run, but to come within a reasonable amount," says Skolnik.
Should you choose sports drinks or water? On runs longer than 60 minutes, sports drinks are a good idea. They have valuable carbs that your muscles need for energy. Skolnik notes they also contain electrolytes like sodium and potassium, which are lost through sweat but are integral to nerve and muscle function, and contribute to your body's water balance.

After Your RunWhen you come in from a run, drink until you're satisfied. "Using thirst as your guide and consuming liquids with your meals is adequate after shorter runs," says Skolnik. If your face has white salt streaks on it postrun, it means you've lost quite a bit of sodium, so it's best to have a sports drink, water with an electrolyte-tablet in it, or water along with food that contains sodium, says Skolnik.

After especially long or hard runs, you also need protein to help your muscles heal. That's why recovery drinks are ideal—they provide protein and fluid to help you rehydrate. "Chocolate milk is a great choice," says Dr. Maharam. "The carbs-to-protein ratio is perfect for recovery."

If you're working out again within 12 hours—say you ran at night and you're planning to run again in the morning—try to be more diligent about rehydrating. Sip liquids regularly until your urine is back to straw yellow and your weight returns to normal.

Eat better: To help reduce the chance of an upset stomach during a race, practice your hydration plan on training runs that mimic your race-day pace.

High-Octane FuelsThese drinks have extra benefits for runners

PrerunCoffee or tea-> Several studies show caffeine can boost endurance.Coconut water-> The clear liquid found in coconuts is packed with the electrolyte potassium.

MidrunElectrolyte tablets-> They dissolve quickly in water and are a low-calorie way to replenish electrolytes; the sodium in them stimulates thirst to promote drinking.Sports drinks-> Carbs provide midrun energy, while sodium helps replace electrolytes lost through sweat.

PostrunVeggie juice-> Good source of sodium to help replace electrolytes.Store-bought recovery drinks-> Convenient source of both carbs and protein to replenish fuel and stimulate muscle repair.Chocolate milk-> Inexpensive and has the ideal carbs-to-protein ratio for muscle recovery.Fruit juice-> High-calorie, so drink moderately. Tart cherry juice has melatonin, which research has found may reduce inflammation when consumed regularly.Smoothies-> Fruit-and-yogurt blends provide anti-oxidants and protein.

To prevent flavor boredom on long runs, consider switching between sports drink and water with an energy gel.

Want to make your own sports drink? Our nutrition editor shows you how: